Travelling wave tubes of the magnetron type



May 6, 1958 REVERDIN 2,833,956

TRAVELLING WAVE TUBES OF THE MAGNETRON TYPE Filed Feb. 17, 1955 2 Sheets-Sheet 1 FIGQZ y 6, 1958 D. REVERDIN 2,833,956

TRAVELLING WAVE TUBES OF THE MAGNETRON TYPE v Filed Feb. 17, 1955 2 Sheets-Sheet 2 and-more particularly to control circuits for Unite TRAVELLING "WAVE TUBES OF THE MAGNETRON TYPE Daniel 'Reverdin, Paris, France, assignor to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Application February 17, 1955, Serial No. 488,752

Claims priority, application France March 11, 1954 6 Claims. (Cl. 315--3.5)

ance with these two applications have given full satisfaction.

However, stabilized direct current supply sources Whose 7 Weight and size are considerable, are necessary for producing'the constant electric fields.

The present invention has for its object to provide pulsemodulated travelling wave tubes of the above-mentioned, "magnetron type in which such direct current supply sources are avoided.

According to the invention, the voltage applied between the electrodes of the interaction space is an alternating voltage synchronized or in phase with the'source ofpulses,

the latter occurring when the field is maximum.

The invention will be better understood from the ensuing description with reference to the accompanying drawings in which:

States Patent Figs. 1 to 4 are axial sectional views of three tubes,

embodying the invention; and

Fig. '5 is an end view of the tube shown inFigs. 1 to 4. Fig. 1 shows a metallic envelope 16' in which are disposed a delay line 4 provided with an ultra-high frequency input 5 and output 6, and a smooth electrode2 parallel with this delay line. An electrode 17 supports the emissive cathode 1. This electrode 17 is in alignment with the electrode 2 and is electrically insulated therefrom.

support 17 forms with the element 3 disposed in front of the cathode and fixed to the envelope, an electron 'lense which concentrates the electronic emission from the cathode 1 into a beam which is propagated '-in the perpendicular to the plane of the figure by a uniform magnetic field provided by a magnet, such as. the .magnet 24 (Fig. '5) and indicated 'in'Figure 1 schematically by the encircled cross. A source of pulses 10 is connected to the primary winding of a transformer 9. The secondary winding of the latter is connected between ground and the heating circuit 18. The latter is connected electrically to the support 17. In this way, when there are no pulses, this support is grounded through the secondary winding of the transformer 9; it is therefore at the potential of the envelope 16 and of the element 3, so that the emission of the cathode is blocked. On the other hand, pulses hav- C "Patented Mayfi, 1958 ing suitable polarity impressedon thesecondary winding of the transformer 9 have for effect to bring the. support 17 to a negative potential relative to the element 3; the

by the source 10 always coincide with a negative peak'of the voltage delivered bythe source 12. The recurrence frequency of the pulses is chosen to'equal the frequency of the voltage applied to the electrode2, or to a frequency which is a sub-multiple of this frequency. If the frequency of the source lz isfor example 1000 C./S., the recurrence frequency of the pulses of the source '10 may be chosen to equal 500 C./S.; the pulses will then be synchronized with each second negative peak of the alternating voltage of the source 12. When the pulse occurs,

the tube will therefore be in normal operational condition.

The supply of alternating current may be obtained by an oscillator, a rotary alternator, or even the main power supply. These sources may supply suitable high voltages through a transformer. Further, all these devices are lighter and easier to stabilize than a direct current supply. The insulating between thesupport 17 forthe cathode 1 and the negative electrode 2 of the interactionyspace is more easily achieved than in the case where the negative electrode is supplied by a direct current. The dielectric strength is indeed greater under alternating than direct current conditions for all known insulating materials. An accidental ionization which may occur in the tube, will be interrupted when the alternating voltage passes through zero. The arcs which might occur between .thecathode 1 and the negative electrode 2 are therefore automatically destroyed.

Fig. 2 shows a modification in which the electric field and the magnetic field are alternating and in phase. In Fig. 2, elements similar to those of the tube shown in Fig. 1 carry the same reference characters. The tube is of the type described in U. S. Patent No. 2,761,088. The electrodes 2 and 4 form in this case a coaxial system having symmetry of revolution; the elec'trodeZ is an axial conductor through which the passage of a current creates a magnetic field whose lines of force are circles around this conductor as shown by the dash concentric circle surrounding the conductor 2. It is understood, of course, that the direction of the lines of force reverses with every reversal or half-cycle of the alternating voltage source. The cathode 1 is insulated from theconductor 2. The envelope 16 has been shown to be made of an insulating material. As in the tube shown in Fig. 1, the cathode 1 is unblocked by pulses applied byvthe source 10 to the transformer 9: the device 13, known per se, synchronizes these pulses with the sourceof alternating voltage 12 which applies to the electrodes-2 and 4 their respective potentials. Further, in this embodiment, 'the same source 12 supplies, through a transformer 14, a first alternating voltage which. is applied between the ends of the conductor, 2, and, througlra, transformer "1'5,"a second alternating voltage applied to electrodes 4 and 2. Thus, the latter carries an alternating current which creates in the interaction space an alternating magnetic field in phase with the electric field existing between the electrodes 2 and 4-. The primary windings of the transformers 14 and 15 are connected in series. Their respective transformation ratios are such that the trans-' p 3 former 15 steps up the voltage and the transformer 14 steps down the voltage. The values of the two fields are therefore always proportional. This ratio of proportionality is determined by the choice of the transformer and of the data of their circuits. The value of the voltage applied to the terminals of the two primary windings determines therefore solely the power applied to the tube and its maximum output power.

In the embodiment shown in Fig. 3, a synchronous motor 18 drives an alternator 12 which applies, as in the case of the tube shown in Fig. 2, suitable voltages to the electrode 4 and to one end of the electrode 2, the other end of the latter being grounded. The lines of force of the alternating magnetic field are again shown in dash lines in this figure, the direction of these lines reversing with every half-cycle of the alternating voltage of the system. Further, the motor 18 drives a rotary switch 13 which comprises a disc on which are disposed grounded studs 20. These studs enter successively into contact with a fixed brush 21 which is connected to the cathode 1. In this way, the cathode is periodically grounded for a short period of time. If the switch 19 and the alternator 12 are keyed in suitable position, this period of time coincides with the positive peak of the voltage applied to the line 4. For the rest of the time, the cathode emission has for effect to cause the potential of the cathode to approach that of the anode 3 and, in consequence, at the end of a short period of time, blocks the emission. The result is the same as that of the preceding devices but there is no longer any need-for a source of pulses 10.

Fig. 4 shows a tube similar to that shown in Fig. 1 in which the cathode 1 is unblocked by pulses of positive polarity applied to an auxiliary electrode 22 facing the cathode and electrically separated from the delay line 4. The pulse operation of such a tube is described in U. S. Patent No. 2,702,370.

In Fig. 4, elements similar to those in the tube shown in Fig. I carry the same reference characters. The magnetic field which may be provided by a magnet 24 illustrated in Fig. 5 is again indicated in Fig. 4 by the encircled cross. The secondary winding of the transformer 9 is here connected between the support 17 of the cathode 1 and the auxiliary electrode 22 which faces the cathode and remains at the same potential as the latter so long as there are no pulses. This electrode 22 is brought to a positive potential relative to thesupport 17 by pulses of suitable polarity, and this causes the beam to be unblocked. The electrode 2 is electrically separated from the cathode 1 and suitably biased by the source 23. The source of alternating voltage 12 is connected between the grounded envelope 16 and the support 17 of the cathode, it brings the unit comprising the electrodes 17, 1, 2 to the negative potential relative to the envelope at the respective instants when the cathode 1 is unblocked by the pulses applied to the electrode 2. The result is the same as in the tube shown in the preceding figures.

In each of the embodiments according to Figs. 1 to 4, an electron-optical system is provided for focusing and concentrating the electrons emitted by a respective cathode into a beam travelling in the space between the electrode 2 and delay line 4 which includes anselement 3 effectively constituting an electron-optical electrode facing a respective cathode 1 and cooperating therewith to produce this result.

What I claim is:

1. In combination with a travelling wave tube of the magnetron type, including an electron emissive cathode, an emission unblocking electrode facing said cathode, and a pair of parallel electrodes extending in a predetermined direction, and defining therebetween an electron and wave interaction space, said cathode and said emission unblocking electrode being positioned to concentrate in a beam travelling in said space, the electrons emitted parallel to said predetermined direction: an alternating voltage source for applying between said parallel electrodes an alternating potential establishing in said space an alternating electric field with lines of force perpendicular to said direction; means for creating in said space a magnetic field with lines of force perpendicular both to said direction and to the lines of force of said electric field; a source of pulses; and means for synchronizing said source of pulses with said alternating voltage source for applying pulses of suitable polarity between said auxiliary electrode and said cathode and unblocking them when said alternating potential has a suitable predetermined intensity.

2. The combination claimed in claim 1, wherein the recurrence frequency of said pulses is equal to said alternating voltage frequency.

3. The combination claimed in claim 1, wherein said magnetic field creating means comprise a source of an alternating current having the same period as said alteranting potential, for generating in said space an alternating magnetic field in phase with said electric field.

4. The combination claimed in claim 1, wherein said alternating voltage source and said source of pulses comprise an alternator, drive means for said alternator, and means driven by said drive means for intermittently biasing said emissive cathode in synchronism with said alternator.

5. The combination claimed in claim 1, wherein said alternating voltage source and said source of pulses comprise a motor driving simultaneously an alternator, and a rotating switch with earthed studs, and connecting means between said switch and said emissive cathode.

6. Incombination with a travelling wave tube of the magnetron type, including an electron emissive cathode, an electron-optical electrode facing said cathode, and a pair of parallel electrodes electrically separated from said cathode-and extending in a predetermined direction and defining therehetween an electron and wave interaction space, said cathode and said electron-optical electrode being positioned to concentrate the electrons emitted from said cathode in a beam travelling in said space parallel to said predetermined direction, a periodic voltage source for applying between said parallel electrodes a periodic potential establishing in said space a periodic electric field with lines of force perpendicular to said direction, means for creating in said space a magnetic field with lines of force perpendicular both to said direction and to the lines of force of said electric field, a source of pulses, and means for synchronizing said source of pulses with said periodic voltage source for applying pulses of suitable polarity between said electron-optical electrode and said cathode to unblock said beam.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,401 Smith Apr. 13, 1948 2,702,370 Lerbs Feb. 15, 1955 2,704,350 Lerbs Mar. 15, 1955 

